BIOLOGY O F SEAWEEDS OF ECONOMIC IMPORTANCE
201
fluctuations will clearly be of importance in order to establish the best
time for harvesting. The principal storage products of marine algae
have been the subject of a recent review (Meeuse, 1962). Studies on the
metabolism of some marine algae by Bidwell (1958), Bidwell et al. (1958)
and Bidwell and Ghosh (1962) have elucidated some of the metabolic
pathways involved. Thus in studies with Fucus vesiculosus using
14C02 it was shown that mannitol was the major soluble photosynthetic
product, and that alginic acid was more rapidly accumulated than either
laminarin or fucoidin. Seasonal fluctuations in the alginic acid content
of the middle lamellae of the cell walls show that this compound is
directly involved in metabolism, and resembles the starch of higher
green plants by its repeated breakdown and re-synthesis. Mannitol
was considered to be more a temporary storage product than an active
metabolite, and there was no evidence that it is a precursor of alginic
acid. Quillet (1954, 1957) considered mannitol and laminarin to be
closely integrated assimilatory products. The different metabolic
pathways in the red algae have been verified by studies on enzyme
activity (Bean and Hassid, 1955; Jacobi, 1962). A critical study of
methods of analysing brown algae has been made by Baardseth and
Haug (1953).
A. Brown algae: the Laminariales
The metabolic products under consideration here are the principal
extractives, e.g. alginic acid, mannitol and laminarin. In the following
pages the times of maximal and minimal production will be described
with regard to the best time of harvesting. The actual quantities of
extractive involved (as yo of dry weight of plant material) are given in
detail in the references from which the data have been drawn, and are
not directly referred to in the succeeding pages. In general, however,
the amounts involved are of the following order. Alginic acid may range
from 8% of the dry weight to values of 40%, the quantities varying
with different seaweeds. With mannitol the range may be from 6% to
I
just over 20%, and with laminarin from less than 1% it0 24%. Some
of the data relevant to this are summarized in Table X.
Regular analyses of three species of Laminaria from the British Isles
were carried out by Black (1948a, 1950, 1954a). Separate analyses
were made of stipes and fronds. With all the species the widest seasonal
fluctuations were shown by the lamina, the seat of assimilation. Thus
with Laminaria hyperborea the alginic acid content of the stipe showed
little seasonal variation, whereas in the frond it was at a maximum
value in the spring and at a minimum in the autumn. Laminarin was
mainly present in the frond, and was at a maximum in the autumn, but
1 .
201
fluctuations will clearly be of importance in order to establish the best
time for harvesting. The principal storage products of marine algae
have been the subject of a recent review (Meeuse, 1962). Studies on the
metabolism of some marine algae by Bidwell (1958), Bidwell et al. (1958)
and Bidwell and Ghosh (1962) have elucidated some of the metabolic
pathways involved. Thus in studies with Fucus vesiculosus using
14C02 it was shown that mannitol was the major soluble photosynthetic
product, and that alginic acid was more rapidly accumulated than either
laminarin or fucoidin. Seasonal fluctuations in the alginic acid content
of the middle lamellae of the cell walls show that this compound is
directly involved in metabolism, and resembles the starch of higher
green plants by its repeated breakdown and re-synthesis. Mannitol
was considered to be more a temporary storage product than an active
metabolite, and there was no evidence that it is a precursor of alginic
acid. Quillet (1954, 1957) considered mannitol and laminarin to be
closely integrated assimilatory products. The different metabolic
pathways in the red algae have been verified by studies on enzyme
activity (Bean and Hassid, 1955; Jacobi, 1962). A critical study of
methods of analysing brown algae has been made by Baardseth and
Haug (1953).
A. Brown algae: the Laminariales
The metabolic products under consideration here are the principal
extractives, e.g. alginic acid, mannitol and laminarin. In the following
pages the times of maximal and minimal production will be described
with regard to the best time of harvesting. The actual quantities of
extractive involved (as yo of dry weight of plant material) are given in
detail in the references from which the data have been drawn, and are
not directly referred to in the succeeding pages. In general, however,
the amounts involved are of the following order. Alginic acid may range
from 8% of the dry weight to values of 40%, the quantities varying
with different seaweeds. With mannitol the range may be from 6% to
I
just over 20%, and with laminarin from less than 1% it0 24%. Some
of the data relevant to this are summarized in Table X.
Regular analyses of three species of Laminaria from the British Isles
were carried out by Black (1948a, 1950, 1954a). Separate analyses
were made of stipes and fronds. With all the species the widest seasonal
fluctuations were shown by the lamina, the seat of assimilation. Thus
with Laminaria hyperborea the alginic acid content of the stipe showed
little seasonal variation, whereas in the frond it was at a maximum
value in the spring and at a minimum in the autumn. Laminarin was
mainly present in the frond, and was at a maximum in the autumn, but
1 .